The present invention relates to methods and apparatus for detecting a specific signal pattern in a signal read from an optical disc.
Many kinds of optical discs utilize the wobble grooves formed on the disc's tracks to determine the disc's address information. As is well known in the art, a digital versatile disc (DVD) records a data's physical addresses utilizing certain specific physical marks formed on the wobble grooves such as phase modulated marks, frequency modulated marks, etc.
The wobble addressing methods adopted for utilization with the DVD discs varying depending on the disc format. For example, DVD-R/-RW discs utilize the land pre-pit (LPP) method, DVD+R/+RW discs utilize the address in pre-groove (ADIP) method, DVD-RAM discs utilize the complementary allocated pit addressing (CAPA) method, and finally the blu-ray discs utilize a combination of the minimum shift keying (MSK) modulation and the saw tooth wobble (STW) as their addressing method.
The pickup head of the conventional optical storage device receives a light beam reflected by the wobble grooves to produce a corresponding wobble signal. Physical marks exist within the wobble grooves and form specific signal patterns within the wobble signal. The optical storage device can obtain the DVD's address information by detecting the specific signal pattern that has been previously formed within the wobble signal.
In the related art, the optical storage device typically utilizes analog techniques to detect the specific signal pattern within the wobble signal. FIG. 1 shows a schematic diagram of a wobble signal having an MSK mark according to the related art. Each MSK mark has a length of three wobble periods. A signal waveform 100 represents a normal waveform of the wobble signal while a signal waveform 120 represents an MSK mark. FIG. 2 depicts a block diagram of a decoding device 200 utilized for detecting the MSK marks within a wobble signal of the related art. The conventional decoding device 200 typically includes two analog mixers 210, 220, two integrators 230, 240, two phase decision units 250, 260, and a single decision unit 270.
The analog mixers 210 and 220 respectively multiply a first encoding frequency φ1(t) and a second encoding frequency φ2(t) on a wobble signal x(t) so as to respectively retrieve wobble signals at specific frequencies. The results from analog mixers 210 and 220 are applied respectively to the integrators 230 and 240. The integrators 230 and 240 continue to perform integrations on wobble signals retrieved by the analog mixers 210 and 220, respectively. The phase decision units 250 and 260 respectively compare a predetermined threshold value with the integrated values from the integrators 230 and 240 to determine the phase of the wobble signal. Finally, the location of an MSK mark within the wobble signal is determined by the decision unit 270 of the decoding device 200 according to the determining results of the phase decision units 250 and 260.
Unfortunately, the analog techniques, commonly referred to as super heterodyne architecture, employed by the conventional decoding device 200 to achieve detection of the MSK marks, increase the complexity of the circuitry designs. Furthermore, when the rotation speed of the optical disc changes, the encoding frequencies φ1(t) and φ2(t) employed in the analog mixers 210 and 220 for mixing the wobble signal should also be modified accordingly. The circuitry control to achieve this further increases the circuitry's complexity. This results in the added difficulty of circuitry control.